UNIVERSITY OF CALIFORNIA. AeRWULWRAL EXPERWEIIT STATION. BULIiETlN NO. 48. Investigations upon the Mercurial Phyl- loxera Remedy. About a year ago much interest was excited by the publication of a statement that finely di- vided ("deadened") quicksilver mingled with the soil around a vine would effectually pre- vent the access of the phylloxera to the roots, and would thus prove a certain preventive of infection, if not a cure for vines already in- fested. In response to numerous inquiries addressed to me on the subject at the time, I stated (see Bulletin No. 18, Oct. 1, 1884) that past experi- ence, as well as direct experiments had shown the inability of the phylloxera to live more than a few hours in the atmosphere created by finely divided mercury in a closed space, or in earth, at the ordinary temperature; and that **the conclusion that a soil column of six or eight inches depth, impregnated with mercurial vapor by intermixture with 'blue mass,' will effectu- ally prevent the passage through it of the slow- going insect, is therefore fully justified." It appears that soon after the publication of the above facts and conclusions, there arose a considerable demand for the preparation of rinely divided mercury, from persous who de- sired to thus protect their vines. Mr. Bauer, the inventor, not having intended to engage in fche business, was unprepared to supply the ma- As to the first point . alluded to above, it should be kept in mind that my prediction of the etfioacy of the application was based upon the condition that (as quoted above) the soil must be *' impregnated loUh mercurial vapor;'' that vapfor, auvl not the liquid mercury, being the effective agent, if from any cause that vapor failed to form, the quicksilver would re main inactive. On teatiug in this respect the mixture fur- nished us by Mr. Bauer, which consisted of equal weights of mercury and clay or chalk, it was found that only the merest trace of mercurial vapor could be detected iu or around it by the most delicate tests; while the same tests showed an abundance of vapor in the mixture prepared in th^ same proportions by ourselves. A corre- spouding difierence manifested itself in the ef- fects on phylloxerated roots, on which the insects were rapidly killed when immersed in our mixture, while in Mr. Bauer's they only showed signs of discomfort and moved off. This puzzling difference was fiually traced to two circumstances which tend to diminish ma- terially the evaporation of the mercury. One is that the metal used was rather scrongly con- taminated with lead^ which is known to retard evaporation in a remarkable degree. The second is that in the preparation of the mixture some oil was used, in order to facilitate the sub- division of the quicksilver, as is frequently done in working on a large scale. Thus each globule ivas coated luith ajilmof oil, which farther inter- fered with evaporation — an effect which, though easily intelligible on physical principles, it was tcnal; but upon being pressed, finally agreed to ^^^^ easy to foresee. And it is quite evident that )repare some of the clay-and-mercury mixture 11 a larger scale. It was thus supplied to a lumber of persons in the infested districts of onoma and Xapa; a number of experiments •ere inaugurated under the auspices of the Vit- ultural Commission; and some 12 vines in the xperimental plot of the University were also leated under Mr. Bauer's directions. These vere, to incorporate a package of the mixture, ontaining about half an ounce of mercury, with bout a peck of soil taken up from around the \ ine, baring its upper roots; then replacing the mercurialized earth. if even the pure mixture acted but feebly on the insects, its interniixture with many times its bulk 01 soil would be still more inert. It was found, however, that iu a number of cases in which neither oil nor the impure mer- cury had been used, the rebults had also been unsatisfactory, while in others the effect of the same mixture bad been prompt, as in the small- scale experiments. Evidently there must have been some other factor concerned in the failures. I had from the outset conjectured that the absorption of the mercurial vapor by the soil itself (analogous to its well kuown disinfecting to the action of the mercury that would vary in different soils. In the case of vapor of water, the amounts taken up by various soils vary from less than one to over twenty per cent of the weight of the soils. If then similar dif- ferences exist in the case of mercurial vapor, some soils — sandy ones — might allow the vapor The failure of at least a large proportion of action in other cases) might be an impediment the applications thus made, to produce , the ex- pected effect within the time it was looked for, ^8 a matter of public notoriety, it having been (diligently heralded both at, home and abroad, '^n advance of any reasonable examination into * e facts and the causes of the discrepant re- Its. • U -1 OV*^ OVUU «l*J^%*J — - The subject was immediately taken in hand within a very short time, being quickly me upon the opening/ of the University ses- saturated; while in the case of loam and clay n, and the investigation is now so far ad- g^^g^ ^-^^^ Yiigh absorptive powers, the slow ced that both the causes of failure, and the pj-Q^ess of evaporation and saturation might oc- --ans to be used in making the remedy etJect- ^^^^ ^ ^^^^ ^j^^e^ during which no free vapor ive on the large, as it was on the small scale, j^Quld be available for action upon the insects. (Q be definitely stated. A detailed account of | r^^ie subject being one that has never been cne experiments will be given in the annual re- j investigated, it was necessary to feel the way port of the department, ' with numerous tentative determinations and" experiments, of which at present some sixty are on record and many more under way. The results, however, have fully verified the correct- ness of the above conjecture, and have also show n the way to make the mercurial applica- tion practically effective for the protection of uninfe.sted vines. Thus, when the finely divided quicksilver is mixed with pure sand in the proportion of about two per cent, the effect on the insects becomes obvious within less than 24: hours after immer- sion; and after six hours more all are dead, or so badly poisoned that they will die even when withdrawn from the sand. But when instead of the sand, a clayey soil is used, having a power of absorption about twelve times greater than the sand, no decided effect is perceived, even after several days. When that same soil, however, after its mix- ture with the mercury, has been subjected for a few hours to the temperature of boiling water, it acts upon the phylloxera as quickly as the sand mixture, and that not only in the labora- tory, but also in the vineyard, as repeated tests have shown. It was also noted that in the lat- ter case the effect did not extend into the natu- ral soil beyond, even to the extent of an inch, in the course of a week; but insects crawling within reach would, of course, perish. These facts having been demonstrated by numerous repetitions of the experiments under varied circumstances, it now remains to apply them to a large scale practice in the vineyard. This part of the subject is still under investiga- tion, so far as the means of readily impregnat- ing large quantities of clayey soil are concerned; but it is even now obvioiv* that Mr. Bauer's original proposition (viz., to protect youmj vine- yards from invasion) is perfectly feasible and conducive to its end, provided sand is used around the stock or cut ing instead of soil, when the latter is at all of a clayey nature. In sandy soils more or less time will elapse before the vapor becomes effective; but it will, never- theless, be likely to afford protection the same season, even without other preparation than in- timate intermixture. But in the case of even moderately clayey soils, a previous preparation to insure saturation icith the metallic vapor, ap- pears to be necessary in order to insure immu- nity from attack during the season in v/hich a cutting has been planted. Even in the preva- lently clayey soils in which the applications in Napa and Sonoma have mostly been made dur- ing the past season, the protective effect will doubtless be felt to a greater or less extent, as the oil Him decays away and the earth becomes gradually saturated. But, while there is every reason to believe that an application once made will remain effective during the life of the vine, so far as the ingress of the insect from above is concerned, it is also clear that the spread in" of the mercury wiH probably t»e toO alow to aSbrdf immunity to outlying roots that may be infected from htloiv. In other words, the mercurial remedy will probably not, as h ;' ! ; 1, avail for the protection of cuti w infested ground, nor for thecun - . aI stocks, unless, perhaps, in very sandy soils. In regard to the practical method for pre- paring siTturatfcd earth in the vineyird, the ex^ perinieuts now in progress seem to show that it can be done by exposing Lhe dr/, fi;ie soil, af^ ter intermixture with the quicitsilver, to hot sunshine such as will maintain its temperature at 110 degrees for from 20 to 30 hours in the ag- gregate (say three to five midsummer days); the- above temperature being the one found to be us- ually assumed by raisins in sun- drying, and hence has been adopted as the standard in our best driers. There are but few parts of California where these conditions cannot be amply fulfilled during some part of the year; and the soil so prepared could then be used at any time when wanted. It is probable that almost any soil might be saturated so as to be available for use in the spring planting, if after mixing in the mercury thoroughly at the beginning of summer, it were left in low piles, protected from the moisture of the ground and air, but accessible to the summer temperature. It should be fully un- j derstocd that the presence of moisture inter- feres materially with the absorption of the va- por by the soil, and therefore with ita satura- tion; although when once saturated, its action on the phylloxera is scarcely interfered with by moderate wetn^^ss.. lo would, of course, be perfectly practicable, in regions where extended planting operations are progressing, to prepare the mercurialized earth more quickly by subjecting the mixture to bteam heat while it is agitated by mechanical means; for instance, by a revolving, spirally- acting agitator within a steam-jacketed, sheet- iron cyhnder, which with the needful small boiler could be -nounted on a waijon truck so as to move about as required. With this, or simi- lar appliances that can readily be devised, at- tention to the avoidance of mercurial poisoning would, of course, be very essential. As to the amount of mercurial vapor actually absorbed and rendered inert by ordinary loam and clay soils, the assays of soifs subjected to the action of vapor only y show that it amounts to from 130 to lliO grains per cubic foot; a rela- tively large quantity, which, considered to- gether with the extremely slow evaporation of the metal at the ordinary temperatures, amply accounts for the observed failures of the remedy as applied heretofore. It is, of course, only the excess over that amount that can produce effect- ive vapor. But as the fourth part of a cubic foot, say 6x6x12 inches, or better, 7x7x9 inches, would constitute an ample application to one vine, the 30 or 40 grains of metal thus rendered inert bear but a ismall proportion to the per- maneut value of the protected vine. On" the whole, the half-ounce dose thus far used by Dr. Bauer, when well mixed in is certainly ample. Experiments on these points, as well as on the effect of vapor saturated soil on the tender rootlets of seedlings, are still in progress, and will be reported in due time. In view of a late discussion concerning the propriety of_^ exterminating the phyl- loxera on tho University vineyard plot, as demanded by the State Viticultural Commission, it is not irrelevant to state that the determination of the above questions would hav^e been altogether impracticable until next season, had not the infested plot afforded the needful material for the numerous experi- ments, and opportunity for daily and hourly observa ion. E. W. Hilgard. Berkeley, Nov. 12, 1SS5.